Active Solders For Solar Panel Manufacture

In recent years, active solders have made their way into use in solar panel manufacture. To understand where S-Bond solder alloys are being used one has to understand the solar panel construction. Solar panels consist of arrays of solar cells, soldered together. A solar cell consists of three basic elements, top contact, base and rear contact, as shown in Figure 1. From the back of each solar cell, electrical contact needs to be made between these surfaces to close the circuit and provide an electron path as photons emit electrons in the semiconductor polysilicon photovolatic (PV) cell which migrate to the back of the exposed cell surface, as illustrated.

Solar Cell IllustrationFigure 1. Illustration of solar cell.

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S-Bond Helping Recycle Water on International Space Station (ISS)

International Space StationCarrying water to the space station is a real challenge and cost, hence recycling water is critical. Waste water, sweat and other ISS water is constantly recycled in a complex system that evaporates and condenses clean water for reuse. For more information on the space station recycling system see the following link: Water Recovery System.

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Myths Regarding Lead-Free Solder Products and Joining Techniques

Soldering Techniques - Joing Methods

Brush Application

While it has been several years since manufacturers began moving to lead-free solder procedures, in part due to the European Union’s Restriction of Hazardous Substances Directive, some still believe myths that have long been inaccurate regarding the use of alloy joining materials that do not require flux and are based on lead and tin.

Temperatures Can Be Enough to Destroy Components

The first round of lead-free solder options to join metals and other materials were comprised of tin, silver and copper, which do have a slightly higher melting point of 217 degrees Celsius compared to existing solder’s 183 degrees Celsius. That disparity could cause problems regarding PC board damage.

However, newer products including several offered by S-Bond have significantly lower melting points that make it easier to join metals like aluminum. At the lowest temperatures, some materials can be joined at just 115 degrees Celsius.

Issues Regarding Silicon Will Require Other Materials

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Solder Bond vs. Epoxy Bond as Thermal Interface Materials (TIM)

Thermal interface materials are materials used in creating heat conductive paths at interfaces between components and thus reduce thermal interface resistance. These materials permit more effective heat flow between separate components where heat is being generated to a heat dissipation components such as solid state transistors to heat sink or a high frequency device connected to a heat spreader. Thermal interface materials’ purpose is to fill the air gap that occurs at contact interfaces with more thermally conductive compounds to permit more effective heat flow than poorly conductive air.

There is a wide variety of thermal interface materials (TIM’s); thermal greases, phase change polymers, thermal tapes, gap filling pads, filled epoxies and solders. All having various costs, performance and manufacturing challenges.

S-Bond Thermal Interface

Figure 1. Illustration of thermal grease filling an interface
between a heat generating device and a heat sink.

Thermal greases are viscous fluid substance which increase the thermal conductivity of a thermal interface “gap by filling microscopic air-gaps present due to the imperfectly flat and smooth surfaces of the components as seen in Figure 1.

Thermal grease compounds have far greater thermal conductivity than air (but far less than metals). They are used in electronics, as depicted in Figure 2, to improve the heat flow from lower power electronic devices thus lowering the components temperature and increasing its life.

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New Lower Temperature Active Solders Developed

S-Bond Technologies has developed and proven a new, lower temperature active solder that melts from 135 – 140°C. The solder, S-Bond® 140 is based around the Bismuth-Tin (Bi-Sn) eutectic composition. This new solder is a lower temperature active solder that enables multi-step soldering where previously soldered connections/seals are not remelted. Active solders that melt below 150C are also finding use in thermally sensitive applications where Sn-Ag based solders that melt over 215°C can thermally degrade the component parts being assembled. Lower temperature soldering also can more effectively bond dissimilar materials where thermal expansion mismatch many times fractures or distorts an assembly’s component parts.

S-Bond 140 is already finding application in glass-metal seals in electronic packages where higher temperature soldering alloys would have damaged the packages’ components. S-Bond 140 is also being used to bond heat pipes and vapor chamber thermal management devices to protect the thermally sensitive phase change fluids from damaging the devices when solder bonding to electronic and LED devices.

Electro-optical package to be bonded to heat sink with S-Bond® 140

Electro-optical package to be bonded to heat sink with S-Bond® 140

Mechanical Activation of Active Solders

Mechanical vs Chemical Fluxing During Solder Bonding

Flux is derived from Latin word fluxus meaning “flow.” In solder joining (also  aluminum soldering, graphite bonding, ceramic to metal brazing, etc.), a flux facilitates wetting by molten metals disrupting oxides on metal surfaces which interrupt the reaction/interaction of the molten solder metals with the underlying metal. Additionally, flux allows solder to flow easily on the working piece rather than forming beads as it would otherwise. Read more about Mechanical Activation of Active Solders